Decoder (Apache Avro Java 1.11.1 API)

java.lang.Object
- org.apache.avro.io.Decoder

Direct Known Subclasses:

BinaryDecoder, ParsingDecoder
```
public abstract class Decoder
extends Object
```
Low-level support for de-serializing Avro values.
This class has two types of methods. One type of methods support the reading of leaf values (for example, readLong() and readString(org.apache.avro.util.Utf8)).
The other type of methods support the reading of maps and arrays. These methods are readArrayStart(), arrayNext(), and similar methods for maps). See readArrayStart() for details on these methods.)
DecoderFactory contains Decoder construction and configuration facilities.

See Also:

DecoderFactory, Encoder

Constructor Summary

Constructors
Constructor and Description

Decoder()

Constructors
Constructor and Description
`Decoder()`

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method and Description
`abstract long`	`arrayNext()` Processes the next block of an array and returns the number of items in the block and let's the caller read those items.
`abstract long`	`mapNext()` Processes the next block of map entries and returns the count of them.
`abstract long`	`readArrayStart()` Reads and returns the size of the first block of an array.
`abstract boolean`	`readBoolean()` Reads a boolean value written by `Encoder.writeBoolean(boolean)`.
`abstract ByteBuffer`	`readBytes(ByteBuffer old)` Reads a byte-string written by `Encoder.writeBytes(java.nio.ByteBuffer)`.
`abstract double`	`readDouble()` Reads a double written by `Encoder.writeDouble(double)`.
`abstract int`	`readEnum()` Reads an enumeration.
`void`	`readFixed(byte[] bytes)` A shorthand for `readFixed(bytes, 0, bytes.length)`.
`abstract void`	`readFixed(byte[] bytes, int start, int length)` Reads fixed sized binary object.
`abstract float`	`readFloat()` Reads a float written by `Encoder.writeFloat(float)`.
`abstract int`	`readIndex()` Reads the tag of a union written by `Encoder.writeIndex(int)`.
`abstract int`	`readInt()` Reads an integer written by `Encoder.writeInt(int)`.
`abstract long`	`readLong()` Reads a long written by `Encoder.writeLong(long)`.
`abstract long`	`readMapStart()` Reads and returns the size of the next block of map-entries.
`abstract void`	`readNull()` "Reads" a null value.
`abstract String`	`readString()` Reads a char-string written by `Encoder.writeString(org.apache.avro.util.Utf8)`.
`abstract Utf8`	`readString(Utf8 old)` Reads a char-string written by `Encoder.writeString(org.apache.avro.util.Utf8)`.
`abstract long`	`skipArray()` Used for quickly skipping through an array.
`abstract void`	`skipBytes()` Discards a byte-string written by `Encoder.writeBytes(java.nio.ByteBuffer)`.
`abstract void`	`skipFixed(int length)` Discards fixed sized binary object.
`abstract long`	`skipMap()` Support for quickly skipping through a map similar to `skipArray()`.
`abstract void`	`skipString()` Discards a char-string written by `Encoder.writeString(org.apache.avro.util.Utf8)`.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - Decoder
```
public Decoder()
```
- Method Detail
  - readNull
```
public abstract void readNull()
                       throws IOException
```
    "Reads" a null value. (Doesn't actually read anything, but advances the state of the parser if the implementation is stateful.)
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and null is not the type of the next value to be read
    
    IOException
  - readBoolean
```
public abstract boolean readBoolean()
                             throws IOException
```
    Reads a boolean value written by Encoder.writeBoolean(boolean).
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and boolean is not the type of the next value to be read
    
    IOException
  - readInt
```
public abstract int readInt()
                     throws IOException
```
    Reads an integer written by Encoder.writeInt(int).
    
    Throws:
    
    AvroTypeException - If encoded value is larger than 32-bits
    
    AvroTypeException - If this is a stateful reader and int is not the type of the next value to be read
    
    IOException
  - readLong
```
public abstract long readLong()
                       throws IOException
```
    Reads a long written by Encoder.writeLong(long).
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and long is not the type of the next value to be read
    
    IOException
  - readFloat
```
public abstract float readFloat()
                         throws IOException
```
    Reads a float written by Encoder.writeFloat(float).
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and is not the type of the next value to be read
    
    IOException
  - readDouble
```
public abstract double readDouble()
                           throws IOException
```
    Reads a double written by Encoder.writeDouble(double).
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and is not the type of the next value to be read
    
    IOException
  - readString
```
public abstract Utf8 readString(Utf8 old)
                         throws IOException
```
    Reads a char-string written by Encoder.writeString(org.apache.avro.util.Utf8).
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and char-string is not the type of the next value to be read
    
    IOException
  - readString
```
public abstract String readString()
                           throws IOException
```
    Reads a char-string written by Encoder.writeString(org.apache.avro.util.Utf8).
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and char-string is not the type of the next value to be read
    
    IOException
  - skipString
```
public abstract void skipString()
                         throws IOException
```
    Discards a char-string written by Encoder.writeString(org.apache.avro.util.Utf8).
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and char-string is not the type of the next value to be read
    
    IOException
  - readBytes
```
public abstract ByteBuffer readBytes(ByteBuffer old)
                              throws IOException
```
    Reads a byte-string written by Encoder.writeBytes(java.nio.ByteBuffer). if old is not null and has sufficient capacity to take in the bytes being read, the bytes are returned in old.
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and byte-string is not the type of the next value to be read
    
    IOException
  - skipBytes
```
public abstract void skipBytes()
                        throws IOException
```
    Discards a byte-string written by Encoder.writeBytes(java.nio.ByteBuffer).
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and byte-string is not the type of the next value to be read
    
    IOException
  - readFixed
```
public abstract void readFixed(byte[] bytes,
                               int start,
                               int length)
                        throws IOException
```
    Reads fixed sized binary object.
    
    Parameters:
    
    bytes - The buffer to store the contents being read.
    
    start - The position where the data needs to be written.
    
    length - The size of the binary object.
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and fixed sized binary object is not the type of the next value to be read or the length is incorrect.
    
    IOException
  - readFixed
```
public void readFixed(byte[] bytes)
               throws IOException
```
    A shorthand for readFixed(bytes, 0, bytes.length).
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and fixed sized binary object is not the type of the next value to be read or the length is incorrect.
    
    IOException
  - skipFixed
```
public abstract void skipFixed(int length)
                        throws IOException
```
    Discards fixed sized binary object.
    
    Parameters:
    
    length - The size of the binary object to be skipped.
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and fixed sized binary object is not the type of the next value to be read or the length is incorrect.
    
    IOException
  - readEnum
```
public abstract int readEnum()
                      throws IOException
```
    Reads an enumeration.
    
    Returns:
    
    The enumeration's value.
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and enumeration is not the type of the next value to be read.
    
    IOException
  - readArrayStart
```
public abstract long readArrayStart()
                             throws IOException
```
    Reads and returns the size of the first block of an array. If this method returns non-zero, then the caller should read the indicated number of items, and then call arrayNext() to find out the number of items in the next block. The typical pattern for consuming an array looks like:
```
   for(long i = in.readArrayStart(); i != 0; i = in.arrayNext()) {
     for (long j = 0; j < i; j++) {
       read next element of the array;
     }
   }
 
```
    Throws:
    
    AvroTypeException - If this is a stateful reader and array is not the type of the next value to be read
    
    IOException
  - arrayNext
```
public abstract long arrayNext()
                        throws IOException
```
    Processes the next block of an array and returns the number of items in the block and let's the caller read those items.
    
    Throws:
    
    AvroTypeException - When called outside of an array context
    
    IOException
  - skipArray
```
public abstract long skipArray()
                        throws IOException
```
    Used for quickly skipping through an array. Note you can either skip the entire array, or read the entire array (with readArrayStart()), but you can't mix the two on the same array. This method will skip through as many items as it can, all of them if possible. It will return zero if there are no more items to skip through, or an item count if it needs the client's help in skipping. The typical usage pattern is:
```
   for(long i = in.skipArray(); i != 0; i = i.skipArray()) {
     for (long j = 0; j < i; j++) {
       read and discard the next element of the array;
     }
   }
 
```
    Note that this method can automatically skip through items if a byte-count is found in the underlying data, or if a schema has been provided to the implementation, but otherwise the client will have to skip through items itself.
    Throws:
    
    AvroTypeException - If this is a stateful reader and array is not the type of the next value to be read
    
    IOException
  - readMapStart
```
public abstract long readMapStart()
                           throws IOException
```
    Reads and returns the size of the next block of map-entries. Similar to readArrayStart(). As an example, let's say you want to read a map of records, the record consisting of an Long field and a Boolean field. Your code would look something like this:
```
 Map m = new HashMap();
 Record reuse = new Record();
 for (long i = in.readMapStart(); i != 0; i = in.readMapNext()) {
   for (long j = 0; j < i; j++) {
     String key = in.readString();
     reuse.intField = in.readInt();
     reuse.boolField = in.readBoolean();
     m.put(key, reuse);
   }
 }
 
```
    Throws:
    
    AvroTypeException - If this is a stateful reader and map is not the type of the next value to be read
    
    IOException
  - mapNext
```
public abstract long mapNext()
                      throws IOException
```
    Processes the next block of map entries and returns the count of them. Similar to arrayNext(). See readMapStart() for details.
    
    Throws:
    
    AvroTypeException - When called outside of a map context
    
    IOException
  - skipMap
```
public abstract long skipMap()
                      throws IOException
```
    Support for quickly skipping through a map similar to skipArray(). As an example, let's say you want to skip a map of records, the record consisting of an Long field and a Boolean field. Your code would look something like this:
```
 for (long i = in.skipMap(); i != 0; i = in.skipMap()) {
   for (long j = 0; j < i; j++) {
     in.skipString(); // Discard key
     in.readInt(); // Discard int-field of value
     in.readBoolean(); // Discard boolean-field of value
   }
 }
 
```
    Throws:
    
    AvroTypeException - If this is a stateful reader and array is not the type of the next value to be read
    
    IOException
  - readIndex
```
public abstract int readIndex()
                       throws IOException
```
    Reads the tag of a union written by Encoder.writeIndex(int).
    
    Throws:
    
    AvroTypeException - If this is a stateful reader and union is not the type of the next value to be read
    
    IOException

Class Decoder

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

Decoder

Method Detail

readNull

readBoolean

readInt

readLong

readFloat

readDouble

readString

readString

skipString

readBytes

skipBytes

readFixed

readFixed

skipFixed

readEnum

readArrayStart

arrayNext

skipArray

readMapStart

mapNext

skipMap

readIndex